Location Pad with Improved Immunity to Interference

ABSTRACT

A location pad includes multiple field-generators, a frame and a mounting fixture. The multiple field-generators are configured to generate respective magnetic fields in a region-of-interest of a patient body, for measuring a position of a medical instrument in the region-of-interest. The frame is configured to fix the multiple field-generators at respective positions surrounding the region-of-interest. The mounting fixture is configured to position the frame above the patient body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 62/504,404, filed May 10, 2017, whose disclosure isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to position tracking systems,and particularly to methods and systems for improving the resilience ofmagnetic position tracking systems to magnetic interference.

BACKGROUND OF THE INVENTION

Magnetic position tracking systems are used in various medicalprocedures, such as in sinuplasty, and are required to withstand varioustypes of interferences.

For example, U.S. Patent Application Publication 2003/0200052, whosedisclosure is incorporated herein by reference, describes a method fordetermining the position of a sensor element, according to which amagnetic alternating field emitted by at least one field generating unitis measured. The inventive method is characterized in interferencefields are calculated, preferably to a first approximation, saidinterference fields being caused by eddy currents produced inelectrically conductive objects. The position that can be determined onthe basis of the signal received in the sensor element is corrected onthe basis of the calculated interference fields.

U.S. Patent Application Publication 2006/0004286, whose disclosure isincorporated herein by reference, describes devices, systems and methodsfor performing image guided interventional and surgical procedures,including various procedures to treat sinusitis and other disorders ofthe paranasal sinuses, ears, nose or throat.

SUMMARY OF THE INVENTION

An embodiment of the present invention that is described herein providesa location pad including multiple field-generators, a frame and amounting fixture. The multiple field-generators are configured togenerate respective magnetic fields in a region-of-interest of a patientbody, for measuring a position of a medical instrument in theregion-of-interest. The frame is configured to fix the multiplefield-generators at respective positions surrounding theregion-of-interest. The mounting fixture is configured to position theframe above the patient body.

In some embodiments, the location pad includes one or more illuminationelements, which are mounted in the frame and are configured toilluminate the patient body. In other embodiments, each of theillumination elements includes one or more light emitting diodes (LEDs).In yet other embodiments, the frame includes transparent material.

In an embodiment, the frame includes transparent material havingexpansion coefficient higher than 74*10⁻⁶ [1/° K]. In anotherembodiment, the mounting fixture is configured to reduce a level ofinterference caused to the magnetic field, by positioning the frame at adistance larger than 5 cm from a metallic part.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for producing a location pad, the methodincludes providing multiple field-generators, which generate respectivemagnetic fields in a region-of-interest of a patient body, for measuringa position of a medical instrument in the region-of-interest. Themultiple field-generators are fixed on a frame, at respective positionssurrounding the region-of-interest. The frame is positioned above thepatient body using a mounting fixture.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial illustration of a sinuplasty surgicalsystem, in accordance with an embodiment of the present invention; and

FIG. 2 is a schematic, exploded view of a location pad for sinuplastyprocedures, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

Embodiments of the present invention that are described hereinbelowprovide improved techniques for reducing interference in magneticposition tracking systems.

Magnetic position tracking systems are used in various medicalprocedures, such as in sinuplasty procedures. In such systems, multiplefield-generators that apply magnetic fields are mounted on a locationpad. A sinuplasty tool that comprises a position sensor is inserted intothe patient nose, and the position tracking system tracks the positionof the sinuplasty tool using the position sensor, which is configured todetect the magnetic fields applied by the field-generators.

In some cases, a position tracking system may be surrounded by metallicparts and/or electrical signals that may interfere with the magneticfields, and degrade the performance of the positioning system. Forexample, in sinuplasty procedures the patient typically sits in anoperating chair comprising metallic parts. Furthermore, the location padmay comprise illumination elements that may interfere with the magneticfields produced by the field-generators. For example, (i) these elementsmay be made from metallic parts and (ii) when lit up, these elementsconduct electrical signals that may interfere with the magnetic fields.

In some embodiments, the location pad is mounted above the patient headso as to set the field-generators far away from the metallic parts ofthe operating chair. In an embodiment, a pillow that supports thepatient head during the procedure, interposes between the location padand the metallic parts of the chair, so as to further reduce the levelof interference caused by the metallic parts of the chair.

In some embodiments, the location pad comprises illumination elements,such as light emitting diodes (LEDs).

During operation, the temperature of the field-generators may increasedue to the electrical currents flowing therein. In an embodiment, thelocation pad comprises a frame, made from materials having low thermalexpansion coefficient, such as Perspex®, which is transparent to passthe light from the LEDs and remains almost un-deformed even atrelatively high temperatures.

System Description

FIG. 1 is a schematic pictorial illustration of a sinuplasty surgicalsystem 20, in accordance with an embodiment of the present invention.System 20 comprises a magnetic position tracking system (not shown),which is configured to track the position of one or more positionsensors in a head 41 of a patient 22.

In some embodiments, the magnetic position tracking system comprisesmagnetic field-generators 44 and one or more position sensors (notshown). The position sensors generate position signals in response tosensing external magnetic fields of field-generators 44, therebyenabling a processor 34 to map the position of each sensor in thecoordinate system of the position tracking system as will be describedbelow.

This method of position sensing is implemented in various medicalapplications, for example, in the CARTO™ system, produced by BiosenseWebster Inc. (Diamond Bar, Calif.) and is described in detail in U.S.Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. PatentApplication Publications 2002/0065455 A1, 2003/0120150 A1 and2004/0068178 A1, whose disclosures are all incorporated herein byreference.

In the present example, system 20 comprises a location pad 40, which ismounted on a chair 28 using a mounting fixture. In the present examplethe mounting fixture comprises a mounting pole 70, although othersuitable types of mounting fixtures can also be used. In an embodiment,pole is configured to mount location pad above patient head 41, which isplaced on a pillow 42 of chair 28. In this configuration, pillow 42 andpatient head 41 interpose between location pad 40 and chair 28.

Reference is now made to an inset 60, which is a view of location pad 40from a tilted perspective. In the present example, system 20 compriseslocation pad 40, which is mounted on a chair 28 using a mounting pole70. In an embodiment, pole 70 is configured to hold the location padabove patient head 41, which is placed on a pillow 42 of chair 28. Inthis configuration, pillow 42 and patient head 41 interpose betweenlocation pad 40 and chair 28.

In some embodiments, location pad 40 comprises multiple field-generators44 fixed on a frame 46. In the exemplary configuration shown in FIG. 1,pad 40 comprises five field-generators 44, but any other suitable numberof generators 44 can be used. In an embodiment, generators 44 arelocated at fixed, known positions external to the patient. System 20further comprises a console 33, which comprises a driver circuit (notshown) configured to drive field-generators 44 with suitable signals soas to generate magnetic fields in a predefined working volume aroundhead 41.

In an embodiment, console 33 comprises a display 36, which is configuredto display an anatomical image 35 obtained using an external imagingsystem, such as a computerized tomography (CT) system (not shown).

In some embodiments, system 20 comprises a sinuplasty tool 30, such as adiagnostic and/or surgical tool, inserted by a physician 24 through anose 26 of patient 22. Tool 30 is used to carry out the sinuplastyprocedure in patient head 41.

In an embodiment, a position sensor (not shown) is coupled to a distalend of tool 30. The position sensor is configured to generate positionsignals indicative of the position of the distal end of tool 30 in thecoordinate system of the magnetic position tracking system.

In an embodiment, processor 34 is configured to register image 35 withthe coordinate system of the position tracking system. The registrationprocess is typically performed before the actual sinuplasty procedure.

In some embodiments, during the sinuplasty procedure, physician 24inserts tool 30 into head 41. Since the CT image is already registeredwith the position-tracking system, physician 24 may navigate the medicaldevice whose distal end is displayed on image 35, to a desired locationin head 41.

In alternative embodiments, instead of receiving image 35 from the CT,processor 34 is configured to receive one or more images acquired usinganother suitable anatomical imaging technique, such as fluoroscopy ormagnetic resonance imaging (MRI), and to register these anatomicalimages with the coordinate system as described above.

Chair 28 typically comprises several parts, such as a base of the chair,adjustable headrest, backrest, seat and their respective motors, ofwhich one or more parts are metallic. In case the location pad would bepositioned under the patient's head, these metallic parts wouldinterfere with the magnetic fields generated by field-generators 44 oflocation pad 40, and therefor degrade the positioning accuracy.

In some embodiments, location pad 40 is fitted above head 41, so as toset it at sufficiently large distance from the metallic parts of chair28 to avoid interference, and yet keep it in close proximity to theposition sensor coupled to tool 30. For example, pole 70 is configuredto hold location pad 40 above patient head 41 at a distance larger than5 cm from metallic objects, such as metallic objects of pillow 42 andchair 28, so as to reduce the level of interference to the magneticfields produced by field-generators 44, without negatively impacting thepositioning accuracy of the position tracking system. Note that pole 70is configured to adjust the distance between pad 40 and metallicobjects, to any suitable value that provides a desired combination ofsufficient illumination and positioning accuracy, at sufficientlyreduced interference.

In an embodiment, processor 34 is typically a general-purpose computercomprising suitable front end and interface circuits for receiving datafrom external sources, as well as measurements from the position sensorof tool 30, via a cable 32, and for controlling other components ofsystem 20. Console 33 further comprises input devices 39 and a userdisplay 36, which is configured to display the data.

FIG. 1 shows only elements related to the disclosed techniques, for thesake of simplicity and clarity. System 20 typically comprises additionalmodules and elements that are not directly related to the disclosedtechniques, and thus, intentionally omitted from FIG. 1 and from thecorresponding description.

Processor 34 may be programmed in software to carry out the functionsthat are used by the system, and to store data in a memory (not shown)to be processed or otherwise used by the software. The software may bedownloaded to the processor in electronic form, over a network, forexample, or it may be provided on non-transitory tangible media, such asoptical, magnetic or electronic memory media.

Alternatively, some or all of the functions of processor 34 may becarried out by dedicated or programmable digital hardware components.

Ear-Nose-Throat (ENT) Location Pad having Improved Resiliance AgainstMagnetic Interference

FIG. 2 is a schematic, exploded view illustration of location pad 40, inaccordance with an embodiment of the present invention. The upper andlower parts of location pad 40 are shown in the upper and lower parts ofFIG. 2, respectively.

In some embodiments, five field generators 44 are fitted into fiverespective recesses 48 of frame 46.

In an embodiment, frame 46 comprises illumination elements 50, such asone or more light emitting diodes (LEDs), fitted in one or more trenches52 formed in frame 46. In some embodiments, illumination elements 50 areadapted to illuminate head 41 of patient 22, so as to assist physician24 in carrying out the sinuplasty procedure.

In some embodiments, one or more conducting cables (not shown) arethreaded through a trench 54 of frame 46, so as to conduct signals tofield-generators 44 and to illumination elements 50. The cables arefitted into trenches 52, and are configured to conduct electricalsignals to field-generators 44 and to illumination elements 50.

In some embodiments, field-generators 44 are configured to operate usingalternating current (AC) signals at a selected frequency, such as 17-19kilohertz (KHz). These operating frequencies are used by the magneticposition tracking system to track the position sensor coupled to thedistal end of tool 30.

The magnetic fields produced by field-generators 44 are subject toexternal and internal interferences that may negatively impact thepositioning accuracy of the position tracking system. The term “externalinterference” refers to interference caused by elements that areexternal to the structure of location pad 40, whereas the term “internalinterference” refers to interference caused by elements that are part ofthe structure of location pad 40.

For example, the metal parts of chair 28 may cause (external)interference to the magnetic field produced by field-generators 44. Insome embodiments, pole 70 is configured to mount location pad 40 at agiven distance from the metallic parts of chair 28, so that pillow 42and patient head 41 interpose between location pad 40 and chair 28,thereby further reducing the level of interference caused by themetallic parts of chair 28.

In some cases, the configuration of location pad 40 may cause internalinterference. For example, illumination elements 50, such as LEDs,typically comprise metal parts that may interfere with the AC fieldsapplied by field-generators 44. The LEDs are typically operated bydirect current (DC) signals that do not interfere with the AC signalstransmitted by field-generators 44.

During operation, field-generators 44 receive power from the drivecircuit of console 33, and may heat up during operation. In someembodiments, frame 46 comprises a transparent material having lowthermal expansion coefficient, such as Perspex®, having thermalexpansion coefficient of 75*10⁻⁶ [1/° K].

In this configuration, frame 46 exhibits an unnoticeable level ofdeformation even when the temperature of field-generators 44 increasesto 100° C. For example, at 100° C. a deformation level of up to 0.84 mmis expected at each edge of a 300 mm long frame (i.e., extending 150 mmto each side of pole 70.)

In other embodiments, frame 46 may comprise any other suitabletransparent material having thermal expansion coefficient higher than74*10⁻⁶ [1/° K].

In some embodiments, location pad 40 is calibrated before applying thesinuplasty procedure, so as to compensate for the internal interferencescaused by the metallic parts of illumination elements 50. In someembodiments, during the calibration, location pad 40 is activated thedistribution of the magnetic field along the entire length of locationpad 40 is measured, e.g., by a scanning robot or any other suitablemeans. In some embodiments, processor 34 is configured to convert thesemagnetic field measurements into a three-dimensional (3D) calibrationmap. In this embodiment, during the sinuplasty procedure processor 34applies the 3D map so as to compensate for the internal interferencecaused to the magnetic fields of location pad 40.

In alternative embodiments, the disclosed techniques can be used,mutatis mutandis, in various other medical procedures applying magneticposition tracking techniques.

Although the embodiments described herein mainly address sinuplastyprocedures, the methods and systems described herein can also be used inother applications, such as neuro-surgery, Ear-Nose-Throat (ENT),Cardiology, ophthalmology, or in any other minimally invasive procedurethat applies magnetic position tracking techniques.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsub-combinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art. Documents incorporated by reference inthe present patent application are to be considered an integral part ofthe application except that to the extent any terms are defined in theseincorporated documents in a manner that conflicts with the definitionsmade explicitly or implicitly in the present specification, only thedefinitions in the present specification should be considered.

1. A location pad, comprising: multiple field-generators, which areconfigured to generate respective magnetic fields in aregion-of-interest of a patient body, for measuring a position of amedical instrument in the region-of-interest; a frame, which isconfigured to fix the multiple field-generators at respective positionssurrounding the region-of-interest; and a mounting fixture, which isconfigured to position the frame above the patient body.
 2. The locationpad according to claim 1, and comprising one or more illuminationelements, which are mounted in the frame and are configured toilluminate the patient body.
 3. The location pad according to claim 2,wherein each of the illumination elements comprises one or more lightemitting diodes (LEDs).
 4. The location pad according to claim 1,wherein the frame comprises transparent material.
 5. The location padaccording to claim 1, wherein the frame comprises transparent materialhaving expansion coefficient higher than 74*10⁻⁶ [1/° K].
 6. Thelocation pad according to claim 1, wherein the mounting fixture isconfigured to reduce a level of interference caused to the magneticfield, by positioning the frame at a distance larger than 5 cm from ametallic part.
 7. A method for producing a location pad, the methodcomprising: providing multiple field-generators, which generaterespective magnetic fields in a region-of-interest of a patient body,for measuring a position of a medical instrument in theregion-of-interest; fixing the multiple field-generators on a frame, atrespective positions surrounding the region-of-interest; and positioningthe frame above the patient body using a mounting fixture.
 8. The methodaccording to claim 7, and comprising mounting in the frame, one or moreillumination elements for illuminating the patient body.
 9. The methodaccording to claim 8, wherein each of the illumination elementscomprises one or more light emitting diodes (LEDs).
 10. The methodaccording to claim 7, wherein the frame comprises transparent material.11. The method according to claim 7, wherein the frame comprisestransparent material having expansion coefficient higher than 74*10⁶[1/° K].
 12. The method according to claim 7, wherein positioning theframe comprises positioning the frame at a distance larger than 5 cmfrom a metallic part so as to reduce a level of interference caused tothe magnetic field.